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    <title>Document</title>
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    <script>
        //1. 内置的全局函数alert
        //alert("我是一个弹出框!");

        //2. 控制台输出
        console.log("<h1>一级标题</h1>");

        //3. 输出内容到网页,能够识别出html标签的
        document.write("<h1>一级标题</h1>")
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